This invention relates to a device and process that provides, in a screening mode, real-time screening and remote imaging, and in an analysis mode, rapid full-area, selective-spectral remote imaging and analysis. More specifically, this invention relates to a device for allowing real-time detection and rapid remote analysis of surfaces with differentiating spectral properties, such as potentially cancerous regions in the cervix, intestine, lungs or other organs.
Cancers, especially cancers in the intestine, cervix, lungs, and other hollow organs, need to be detected early for effective treatment. For example, intestinal cancers typically start with polyps, either protruding (pedunculated tubular adenomas) or flat (sessile villous adenomas). These polyps sometimes convert into cancer. Therefore, the detection or removal of polyps by colonoscopy significantly reduces the risk of getting colon cancer. Traditionally, polyps are detected using devices that allow a physician to visually examine the interior of the intestine. However, because of the large interior surface area of the intestine, such examinations need to be carried out at a rapid rate so that the maximum area of the intestine can be examined in a minimum amount of time. Further, the amount of time for such examinations must be minimized in order to minimize the expenses and physical impact of such examinations. It is also more difficult to detect flat polyps (sessile villous adenomas) with such examinations.
Two major types of procedures for intestinal examination are sigmoidoscopy and colonoscopy. In these procedures, a device for viewing the interior of a hollow organ, usually an endoscope, is inserted into the intestine through the anus. The endoscope usually includes input from a light source and includes lenses at the end of a long flexible cable. An imaging bundle of coherently bundled optical fibers is usually provided inside the cable to transmit an image with a resolution determined by the number of fibers in the bundle. The field of view of an endoscope can be 45 to 140 degrees, depending on the lenses selected. Some endoscopes also have a biopsy channel in the cable that allows the examining physician to extract a tissue sample, such as a portion of a polyp, for later analysis, such as by a biopsy (or even to extract an entire polyp). In sigmoidoscopy, the patient is conscious during the examination, and therefore, the time for the examination must be minimized to minimize the patient""s discomfort during the procedure. Further, sigmoidoscopy does not screen the entire length of the intestine because a sigmoidoscope does not pass beyond a 120-degree bend in the intestine called the left colic (splenic flexure). In a colonoscopy, the entire length of the intestine can be screened, but the patient must be fully anesthetized, which introduces all the attendant risks of anesthetization. Traditional visual analysis of polyps and other colonic lesions requires training and experience. Because polyps are small, and not all polyps are cancerous, it is helpful to somehow mark pre-cancerous polyps or other abnormal tissues to enhance viewing and detection while screening. It is desirable to reduce the overall number of biopsies because there is an increased risk of morbidity with each additional biopsy.
Fluorescence is a well-known phenomenon in which an excitation light of one wavelength causes a material to emit fluorescent light of a different wavelength. For example, household fluorescent lamps are glass tubes filled with mercury vapor and interiorly coated with phosphor, having electrodes at both ends. When the electrodes are energized with electricity, they emit electrons, which strike the atoms of mercury vapor to cause those atoms to emit ultraviolet light. The ultraviolet light (the excitation light) then strikes the phosphor, which causes the phosphor atoms to emit white light (the fluorescent light). For another example, so-called xe2x80x9cblack lightxe2x80x9d is actually ultraviolet light that causes certain materials to emit visible light.
Visible light is considered to have wavelengths of between approximately 400 and approximately 760 nanometers (billionths of a meter, or xe2x80x9cnmxe2x80x9d). Light having wavelengths shorter than approximately 400 nm is considered to be ultraviolet light by the United States Food and Drug Administration and other countries"" regulatory agencies. More specifically, UVA radiation is considered to range from approximately 315 nm to approximately 400 nm, UVB radiation is considered to range from approximately 280 nm to approximately 315 nm, and UVC radiation is considered to range from approximately 100 nm to approximately 280 nm. UVA radiation is sometimes referred to as long wave ultraviolet or xe2x80x9ctanning rays.xe2x80x9d UVB radiation is considered to be more dangerous than UVA and causes damage to genes, and UVC radiation is considered to be even more dangerous than UVB because of its shorter wavelength and higher energy. Thus, the power and allowable time for exposing patients to light having wavelengths of less than 400 nm is restricted. However, there are no such restrictions on exposing patients to visible light.
Although the human eye cannot see light having wavelengths shorter than about 400 nm, some imaging devices, such as certain types of CCDs (charge coupled devices) can detect light down to approximately 360 nm or lower.
It has been discovered that when tissues are excited by a certain excitation light (such as ultraviolet or blue or violet light) the fluorescent light emitted by abnormal tissues has a spectrum (including in the visible range) that differs from the fluorescence spectrum of normal tissues at certain differentiating portions (or bands) of the color spectrum. This is because types and/or amounts of various substances (each having distinctive fluorescence spectra) differ in abnormal tissues from those in normal tissues. This phenomenon of fluorescence due to natural characteristics of the tissues is known as xe2x80x9cautofluorescencexe2x80x9d. The naturally occurring substances in tissues that fluoresce when excited are referred to as xe2x80x9cendogenous fluorophores.xe2x80x9d
Another type of fluorescence that may be utilized in cancer detection is induced fluorescence, that is, fluorescence induced by administration of an exogenous (that is, introduced from outside the patient) fluorescent marker (or exogenous fluorphore) that selectively localizes in abnormal precancerous and cancerous tissues. Thus, the abnormal tissues will fluoresce at a particular marker wavelength (or set of wavelengths) when those tissues are illuminated with an excitation light that causes the exogenous fluorescent marker to fluoresce. An example of an exogenous fluorescent marker is 5-aminolaevullinic acid (xe2x80x9cALAxe2x80x9d). ALA induces precancerous and cancerous tissue to preferentially accumulate protoporphyrin IX (xe2x80x9cPpIXxe2x80x9d). PpIX is a photosensitizer, but clears rapidly from the body, limiting the period of enhanced tissue sensitivity to between 24 and 48 hours. When excited with a marker excitation light having a wavelength of around 400 nm, PpIX emits a marker fluorescent light having a characteristic fluorescence spectrum with peaks centered at approximately 635 and 700 nm. In addition, PpIX occurs naturally in humans and causes few side effects.
The intensity of autofluorescence is fairly weak, relative to induced fluorescence, and can be difficult to detect, requiring a longer time for exposure, much as a photograph in weak light requires a long time exposure. Accordingly, it is desirable to use relatively bright light in the visible range (such as blue or violet light) or in the portion of the UVA range near 400 nm to apply enough excitation light to make autofluorescent light bright enough for rapid acquisition of autofluorescence images. Rapid acquisition of images is desirable to avoid blurring due to patient movement, minimizing time for examination, and for other reasons. It is not practical to use high intensity, long duration ultraviolet light to increase the intensity of autofluorescence because such high intensity, long duration ultraviolet light may damage a patient""s tissues. Further, there is often a maximum response of fluorophores to excitation light, so that higher intensity excitation light yields little additional emitted autofluorescent light. Also, ultraviolet light can be used only if regulatory requirements, such as limited exposure doses, can be met. In some cases, shorter-wavelength radiation can enhance the autofluorescence signal. However a shorter wavelength light also may increase the risk of damage to a patient""s tissues and may be subject to even more stringent regulatory requirements.
Preferably, when induced fluorescence is used, the marker fluorescent light emitted by the exogenous fluorescent marker is much brighter than the autofluorescence emitted by the tissues to allow for comparatively faster image acquisition, which in turn allows for rapid screening for potentially abnormal (suspicious) tissues.
Prior screening methods using ALA were employed to find potentially cancerous lesions or polyps, and a biopsy was then extracted from the tissue to confirm a diagnosis. However, taking a tissue sample creates a risk of cramping, infection, excessive bleeding or perforation, and may be completely out of the question for certain people, such as hemophiliacs or others with impaired clotting ability or immune systems.
Instead of administering ALA (or other exogenous fluorescent marker), screening can be accomplished by creating video images of tissues in visible light and using image processing techniques to indicate areas of potential interest, as described in more detail below, thus providing automated visual screening with increased accuracy and consistency (as compared with manual visual screening).
Of course, both methods could be combined, by administering ALA (or other exogenous fluorescent marker), illuminating the tissues with a marker excitation light to induce marker fluorescence of the ALA (or other exogenous fluorescent marker), and then applying automated screening to the marker image formed by the marker fluorescence.
The differentiating portions of the autofluorescence spectra of normal and abnormal tissues may be faint, so a substantial amount of time is needed to acquire autofluorescence spectral data for analysis. A disadvantage of spectroscopy of a single point is that areas must be spectrally analyzed point by point to delineate the spatial extent of any abnormal tissue. Further, the differentiating portions of some of the fluorescing spectra may be narrow (such as ALA""s spectral peaks), so that high spectral resolution may be needed to resolve those particular differentiating portions. Some of the differentiating portions may not need a high spectral resolution, however.
Standard color cameras employ three broad and overlapping red, green and blue bands. Optical devices which detect radiation in multiple bands not confined to the standard three bands are conventionally classified as either hyperspectral or multispectral devices. A spectral resolution of 10 nm or less, with 20 or more spectral bands, is conventionally called hyperspectral resolution. Multispectral analysis conventionally refers to analysis of multiple spectral bands, which may be contiguous or non-contiguous and of different widths, but conventionally implies non-hyperspectral resolution, that is, resolution that does not reach 10 nm or less.
An article entitled xe2x80x9cEndoscopic fluorescence imaging and point spectroscopy system for the detection of gastro-intestinal cancersxe2x80x9d by Nadeau, V. et al, Journal of Modern Optics, 2002, Volume 49, pages 731-741, incorporated herein by reference, discloses a combined endoscopic fluorescence imaging and point spectroscopy system for detecting gastrointestinal cancers utilizing the fluorescence from PpIX. This Nadeau reference teaches the use of point spectroscopy by measuring the full fluorescence spectrum from a single point by passing an optical fiber down the biopsy channel of an endoscope and placing it in contact with the tissue. In the point spectroscopy mode, the fiber optic abuts against the region of interest and the acquired light is then spectrally analyzed, apparently without forming an image remotely (there is no suggestion that the fiber optic consists of multiple fibers that are coherently bundled so as to be capable of forming images). The spectrometer provides xe2x80x9ca signal resolution of 10 nm over the range 350 nm to 850 nm.xe2x80x9d The area of coverage for point spectroscopy therefore depends on the size of the fiber optic that abuts against the tissue, which may make determination of the extent (i.e., perimeter) of the abnormal tissue difficult.
An article entitled xe2x80x9cAn endoscopic fluorescence imaging system for simultaneous visual examination and photodetection of cancersxe2x80x9d by Wagnieres, G., et al., Rev. Sci. Instrum., Vol. 68, No. 1, January 1997, pages 203-212, incorporated herein by reference, discloses a fluorescence endoscope in which the fluorescence contrast between the tumor and surrounding normal tissue is enhanced by real time image processing by simultaneously recording the fluorescence image in two spectral domains, after which the images are digitized and manipulated with a mathematical operator (look-up table) at video frequency. The device also allows for immediate observation of the endoscopic area under white light illumination during fluorescence detection in order to localize the origin of positive fluorescence signals.
An article entitled xe2x80x9cAn endoscopic system for the early detection of cancers of the gastrointestinal tractxe2x80x9d, McKechnie, T., et al., Rev. Sci. Instrum., Vol. 69, No. 6, pages 2521-2523 (June 1998), incorporated herein by reference, discloses a 3-color camera, an intensified CCD camera and an fiber-coupled spectrometer, all of which are simultaneously mounted on a standard endoscope. This device specifically allows the operator to record a full optical spectrum of a particular region of a tissue.
An article entitled xe2x80x9cAn endoscopic imaging system for the early detection of cancerxe2x80x9d by Padgett, M., and Sibbett, W., incorporated herein by reference, discloses the use of ALA as a fluorescent marker with a miniature color camera to provide a navigation image under normal white light illumination and an intensified camera filtered to detect light between 630 and 640 nm, i.e., an image showing only PpIX fluorescence.
U.S. Pat. No. 5,590,660 to MacAulay, et al., incorporated herein by reference, discloses an apparatus employing a light source for producing excitation light to excite the tissue to generate autofluorescence light and also for producing illumination light. A filter acts to integrate the autofluorescence image over a range of wavelengths in which the autofluorescence intensity for normal tissue is substantially different from the autofluorescence intensity for diseased tissue to establish an integrated autofluorescence image of the tissue. A monitor then displays the integrated autofluorescence image and the remittance light image to produce a normalized image in which the diseased tissue is distinguishable from normal tissue.
U.S. Pat. No. 5,507,287 to Palcic, et al., incorporated herein by reference, discloses a light source for generating excitation light that includes wavelengths capable of generating characteristic autofluorescence from abnormal and normal tissue. An imaging bundle collects autofluorescence light from the tissue, which is then filtered into spectral bands by a filter wheel. For one of the spectral bands, the autofluorescence intensity for abnormal tissue is substantially different from normal tissue, while for the other spectral band the autofluorescence intensity for abnormal tissue is substantially similar to that for normal tissue. An optical system intercepts the autofluorescence light to acquire at least two filtered emitted autofluorescence images of the tissue. These acquired images are displayed in real time on a display monitor so as to delineate abnormal and normal tissue. Synchronizing means are disclosed to allow for alternate illumination of the tissue by laser light and a white light source. However, Palcic indicates that one transformation which has been reported with tumor localizing drugs was found not to be useful for the imaging method.
U.S. Pat. No. 6,236,881B1 to Zahler, et al., incorporated herein by reference, discloses a computerized apparatus implementing a real time detection algorithm for non-drug activated imaging of diseases. A metal halide light source produces excitation light to excite the tissue to generate combined reflection and autofluorescence light. An optical system coupled to a digital color and multispectral camera collects the combined reflection and autofluorescence light for the inspected tissues. The system contains a miniature filter wheel, running synchronously with the camera video frame for real time buffering and multitasked spectral and spatial segmentation algorithm implementations.
U.S. Pat. No. 6,160,618 to Garner, incorporated herein by reference, discloses a hyperspectral slide reader in which an imaging spectrometer is positioned in the path of a light from the side to split the light line into a light array, and the camera can detect the entire spectrum of light produced by the imaging spectrometer.
U.S. Pat. No. 5,782,770 to Mooradian, et al., incorporated herein by reference, discloses techniques and devices for diagnosing tissue via hyperspectral imaging in which a 3-dimensional image is formed where two dimensions contain information about an area, and one dimension contains full spectral information for that area. The spectral content of the image can be analyzed on a pixel by pixel basis to determine the presence of certain matter and the spatial extent thereof.
Published Patent Cooperation Treaty International Patent Application PCT/US94/00702 (International Publication No. WO94/16622), incorporated herein by reference, discloses an apparatus that produces a diagnostic image by exposing a live tissue specimen in situ to a primary light, selecting particular wave lengths of secondary light returned from the examined tissue, and obtaining one or more sequential images from the examined tissue.
U.S. Pat. No. 5,379,065 to Cutts, incorporated herein by reference, discloses a hyperspectral imager including a focal plane having an array of spaced image recording pixels, an electronic shutter and an electronic spectral filter for selecting a spectral band of light received by the focal plane and an electronic controller, controlling the rate at which a recording is transported in the longitudinal direction, the exposure time and the spectral bands so as to record a selected portion of the scene through M spectral bands with a respective exposure time tq for each respective band q.
U.S. Pat. No. 5,413,108 to Alfano, incorporated herein by reference, discloses a method and apparatus for examining a 2-dimensional region of a tissue sample by exciting the tissue sample with light at a first wavelength and measuring the resultant fluorescence at an emission wavelength. The two-dimensional region is then illuminated again at a second wavelength, and the resultant fluorescence is measured at the same emission wavelength. The two wavelengths are chosen so that the ratio or difference of fluorescence intensities at the emission wavelength is indicative of the carcinomatous condition of the tissue.
The process of this invention comprises providing an area that contains both normal and abnormal tissues with an exogenous fluorescent marker that selectively localizes in abnormal tissue and that fluoresces (preferably brightly) at a particular marker wavelength when illuminated by an excitation light. Imaging light (preferably white visible light) is then filtered to remove light of that marker wavelength to result in markerless imaging light. Of course, alternative means for creating markerless imaging light can also be used, such as using multiple broadband light sources that do not emit light at the marker wavelength, one emitting light at shorter wavelengths and the other emitting light at longer wavelengths. In a screening mode, the area is illuminated with both markerless imaging light and an excitation light, so that the exogenous fluorescent marker in the abnormal tissue is induced to fluoresce (preferably brightly enough that the fluorescent light can be detected even though the tissues are simultaneously illuminated with an imaging light) at the marker wavelength. Light at the marker wavelength is then separated to form a marker image, while the remaining light forms a background image, over which the marker image is preferably overlaid, displayed side by side, or displayed alternately. The user can thus rapidly scan for areas of potential interest (suspicious areas), avoiding the delay of analyzing areas that do not fluoresce at the marker wavelength.
Instead of using a fluorescent marker, screening can be performed automatically by creating a video image of the tissues in visible light using the imaging light (optionally including ultraviolet light down to approximately 360 nm) and then using image processing techniques to indicate areas of potential interest (pre-segment the scene) in preparation for the analysis mode, as described below. Of course, if this automatic screening using image processing of visible light images is used, without administration of ALA (or other exogenous fluorescent marker), then there is no need for a marker filter. This automatic screening using image processing techniques can also be combined with the use of an exogenous fluorescent marker. Screening can also be performed with conventional visual examination.
If an area of potential interest (suspicious area) is found during the screening mode (either by automatic image processing of a visible light image to pre-segment the scene, or by fluorescing at the marker wavelength, or conventional visual examination), the user can activate an analysis mode (a xe2x80x9cvirtual biopsyxe2x80x9d) in which that area is illuminated only with the (preferably ultraviolet) excitation light, and the resulting autofluorescence light is remotely imaged at multiple narrow spectral bands selected to differentiate normal from abnormal tissues (and optionally a reference band for normalization), so that full area images at selected spectral bands are formed, whereby collecting full spectral information is avoided. This is referred to as xe2x80x9cfull-area, selective-spectralxe2x80x9d imaging. Preferably, the resolution of at least one of the selected spectral bands is 10 nm or less, but this is not necessarily always the case. Preferably at least some of the selected bands are non-contiguous, but surprisingly, as noted below, contiguous or overlapping bands may be preferred if they discriminate efficiently between normal and abnormal tissues. These full-area, selective-spectral images can then be analyzed to differentiate the abnormal tissue from normal tissue, thus constituting a selective-spectral analysis.
Because only selected portions of the autofluorescence spectrum are collected, collection of the remaining portions of the autofluorescence spectrum is avoided, so that the process is much faster than prior art processes, which take the time to collect full spectral data, and then discard unused portions. Avoiding the collection of spectral data unnecessary or superfluous for differentiating normal from abnormal tissues allows for rapid acquisition of the autofluorescence spectral data that is necessary for such differentiation and hence for rapid analysis, that is, analysis in near real time, or approximately in real time. The term xe2x80x9creal timexe2x80x9d refers to a time brief enough that it is easily incorporated into the examination sequence, such as less than approximately 5 seconds per scan or analysis. The terms xe2x80x9cnear-real timexe2x80x9d or xe2x80x9capproximately in real timexe2x80x9d or xe2x80x9capproximate real timexe2x80x9d or xe2x80x9crapidxe2x80x9d refer to time spans short enough that multiple analyses are available quickly enough to be usable within the time of a typical medical examination, such as less than approximately 30 seconds per analysis.
Because it is not necessary to contact the tissue in either mode, the process allows remote imaging and analysis.
The device of the invention is a device that includes an imaging light source emitting imaging light and an excitation light source emitting excitation light. Preferably, a user-activatable shutter (or other means to regulate light output) is provided to selectively block the imaging light. The user thus controls what mode is employed. Alternatively, either or both of the imaging light source and excitation light source can be light emitting diodes or LEDs (preferably temperature stabilized to preserve spectral purity by avoiding spectral fluctuations caused by warming up and cooling down) with power that is switched or cycled on or off as modes are changed by the user, which eliminates a mechanically moving part.
Of course, either or both of the imaging light source and excitation light source can also be any other kind of light, such as a lamp, including an arc lamp, quartz-halogen lamp, or other lamp, or laser. The imaging light is preferably white visible light with an approximately flat spectral output from approximately 360 nm to approximately 760 nm, and the excitation light is preferably selected from either blue or violet light or ultraviolet light. An optical combiner, such as a dichroic mirror (a mirror that passes some wavelengths and reflects others), then combines the imaging light (when turned on or when not blocked by the shutter) and the excitation light. Of course, the optical combiner can be separate fiber optic bundles for the markerless imaging light and for the excitation light that are combined in the light guide, or other alternatives, as well. Optionally, if a fluorescent marker will be used, a narrow band filter (marker filter) removes light at a marker wavelength from the imaging light, resulting in markerless imaging light. A light guide then directs the markerless imaging light and the excitation light onto the tissue so that the tissue is selectively illuminated with either (in an analysis mode) the excitation light alone (the imaging light is turned off or blocked by the shutter), or (in a screening mode) both the excitation light and the markerless imaging light (the imaging light is turned on or is not blocked by the shutter). Of course, other alternatives for selectively illuminating the tissues with the excitation light and/or the markerless imaging light can be used.
If an exogenous fluorescent marker has been previously administered (such as by injection, ingestion, or otherwise), during the screening mode, the excitation light induces abnormal tissue to fluoresce brightly enough at the marker wavelength to be visible when the tissue is simultaneously illuminated with markerless imaging light. During the analysis mode, the abnormal tissue autofluoresces differently from the normal tissue at differentiating portions of the tissue""s fluorescent spectrum.
An imaging bundle is positioned to transmit an image of the tissue as it autofluoresces during the analysis mode, preferably starting at a wavelength just above the wavelength of the excitation light, such as (for example) 360 nm. Of course, the imaging bundle also transmits an image of the tissue as it is illuminated by the imaging light (and simultaneously by the excitation light if induced fluorescence is being used) during the screening mode. An adjustable narrow band filter is operably connected to the imaging bundle that:
in a screening mode (with the shutter open or the imaging light on), directs fluorescent light at the marker wavelength emitted from the tissues to a sensitive (preferably) monochromatic imaging device (such as a CCD, CMOS, or equivalent) to form a marker image, and that directs reflected light from the tissues to a color or black and white, preferably high resolution, imaging device (such as a color CCD, CMOS, or equivalent) to form an imaging image; and
in an analysis mode (with the shutter blocking the imaging light or the imaging light off), deflects only multiple selected (preferably narrow) bands of the differentiating portions of the autofluorescence spectrum (and optionally a reference band) to the monochromatic imaging device to form multiple selective-spectral images.
An image processor is then operably connected to the imaging devices that combines data from the imaging devices in approximately real time that:
in the screening mode, creates a false color overlay of the marker image from the monochromatic imaging device over the imaging light image from the high resolution imaging device; and
in the analysis mode, analyzes multiple selected (preferably narrow) bands of differentiating portions (and optionally a reference band) of the autofluorescence spectrum and differentiates the normal tissue from the abnormal tissue to create a differentiated image of the abnormal tissue. The image processor can be operably connected to a display device, such as a monitor, and the differentiated image of the abnormal tissue can be displayed over the imaging light image from the high resolution imaging device. Optionally, the selected spectral bands of the differentiating portions can be displayed in selected false colors to enhance visual detection of abnormal tissue. Of course, instead of overlaying the images, other means for visual comparison can be used, such as displaying the images side by side display, or alternating images.
Thus, in the screening mode, the tissue is illuminated by both the imaging light and the excitation light, but in the analysis mode, the tissue is illuminated only by the excitation light. Alternatively, if automated visual screening is performed by pre-segmenting the scene using image processing, the tissue is illuminated only with imaging light during the screening mode, and only by the excitation light during the analysis mode.
The device combines the speed of screening using an exogenous fluorescent marker (or pre-segmenting the scene using image processing) with (when the user selects) the ease and accuracy of using spectral analysis to confirm that a suspicious area is cancerous (thus avoiding the need for a biopsy). Further, because the device avoids collecting unnecessary or superfluous spectral data during the analysis mode, the analysis can be performed rapidly, in near real time or approximately in real time.
The imaging of both imaging devices preferably preserves all spatial information, such as shape and texture. The imaging devices can be operably connected to display devices, such as monitors, to display full-area images of the tissues in both modes.
It is preferred that the imaging light extend to ultraviolet wavelengths overlapping the excitation light spectrum (or the shortest wavelength of autofluorescence) so that at least a portion of the resulting imaging image is collected at the same wavelengths as the autofluorescence image. This allows both the imaging image and the autofluorescence image to be co-registered, that is, accurately aligned with each other.
With the above invention, a process and device are provided that allow for rapid remote screening, using ALA (or other exogenous fluorescent marker) to indicate the location of potentially abnormal (suspicious) tissue while screening. This screening mode allows real time or near real time screening of large areas of tissue by illuminating the tissue with both markerless imaging light and excitation light, which stimulates emissions at a marker wavelength or wavelengths. In the optical system described above, the excitation light causes the exogenous fluorescent marker to fluoresce at the marker wavelength(s) to form a marker image and the markerless imaging light reflects off the tissues to form an imaging image. The term xe2x80x9cmarker imagexe2x80x9d denotes the image formed using the marker fluorescent light emitted by the tissues, preferably displayed on a sensitive monochromatic imaging device. The term xe2x80x9cimaging imagexe2x80x9d denotes the image formed by the markerless imaging light reflected from the tissues, preferably displayed on a high-resolution color (or other multiple chromatic) imaging device. The marker image can be overlaid on the imaging image (or displayed side by side or alternated) to show areas of potential interest (suspicious area).
Alternatively, automatic screening can be accomplished by scene segmentation using image processing techniques, such as fractal pattern recognition in the spatial domain (classifying or segmenting a scene by image characteristics such as granularity or degree of border irregularity), classifying or segmenting a scene by morphology, classifying by the shapes of regions, texture or color, and other image processing methods now known or later developed. With this automatic screening by scene segmentation, only the high-resolution imaging device need be used during the screening mode because the screening can be performed using the full spectral range of the imaging image. However, if scene segmentation can be more efficiently or effectively conducted over specific spectral range(s), then the adjustable narrow band filter can divert a selected spectral band or bands to the monochromatic imaging device during the screening mode as well as during the analysis mode.
If screening is accomplished using ALA (or another exogenous fluorophore), it would be preferred to have two excitation lights, a marker excitation light emitting light (referred to as marker excitation light) at the optimal excitation wavelength for the exogenous fluorophore during the screening mode, and an autofluorescence excitation light emitting light (referred to as autofluorescence excitation light) at the optimal excitation wavelength for stimulating autofluorescence during the analysis mode. Of course, two shutters could then be provided, so that during the screening mode, an autofluorescence shutter blocks the autofluorescence excitation light and the tissue is illuminated only with marker excitation light and the imaging light, and during the analysis mode, a marker shutter blocks the marker excitation light (and the imaging light has been blocked as well) and the tissue is illuminated only with autofluorescence excitation light. Of course, if the excitation lights are cycled between modes by having their power turned on or off, then no shutters would be necessary. Alternatively, some or all of the shutters could also be combined into one shutter with aperture(s) that alternate between the excitation lights (and the imaging light).
If the screening mode finds an area of potential interest (suspicious area), the device can change to analysis mode and illuminate the tissue only with excitation light and then analyze only the differentiating portions of the autofluorescence spectra of the tissues (and optionally a reference band) according to well-known characteristics, such as ratio of spectral peaks, intensities, etc. Other analysis methods, such as fractal pattern recognition in the spatial domain, morphology analysis, and other modes that are developed in the future, also can be used. Preferably, the analysis mode is accomplished through rapid cycling through multiple selected spectral bands. Preferably the spectral bands can be selected to be non-contiguous, contiguous or overlapping. This analysis is fast enough for approximately real time spectral analysis, although enough time must be allowed to acquire and integrate multiple bands of autofluorescence signals, which are weaker than the induced fluorescent signals used in the screening mode.
Area imaging and a sensitive imaging device (such as a CCD) are used to rapidly acquire high-resolution images to allow rapid, almost real time analysis. This invention thus avoids the need for actual biopsies, reducing pain, cost and the risk of infection. Greater optical throughput, decreased image capture time, and reduced blurring (or lost data) from the patient""s movements are achieved. This is by contrast to xe2x80x9cpushbroomxe2x80x9d imaging, in which full spectral data sets are collected and then filtered (which sometimes results in collecting and discarding substantial amounts of unneeded data). Pushbroom imaging also entails a substantial possibility of blurring due to patient movements.
For example, in the present invention, if 5 spectral bands, starting at a wavelength just above the excitation light wavelength or longer (such as starting at 360 nm or longer), each band being approximately 10 to 20 nm wide, are selected for analysis (to determine the differentiating portions of the spectra between normal and abnormal tissues), then approximately 50 to 100 nm of spectral data would be collected in total. Because the full visual spectrum spans approximately 360 nm (400-760 nm), collecting only approximately 50 to 100 nm of spectral data would mean collecting only about one-eighth to about one quarter of the full visible-light fluorescence spectrum available. However, because these bands would be selected to determine the differentiating portions of spectra between normal and abnormal tissue, collecting data only from these bands would be sufficient to differentiate between normal and abnormal tissue. This would mean therefore that collecting the necessary spectral data for analysis would only take approximately one-fourth to one-eighth of the time (or would be 4 to 8 times faster) than collecting the full spectral data, as would be done with conventional pushbroom scanning. Collecting spectral data 4 to 8 times faster would proportionately reduce the examination times and blurring, as compared to pushbroom or other technologies that collect full spectral data.
Moreover, if the excitation light is ultraviolet, patients are exposed to less ultraviolet light because examination times are reduced. In addition, because ALA induces accumulation of the photosensitizer PpIX (or another photosensitizer may have been administered to the patient), collecting spectral data faster by using selective spectral (instead of full spectral) imaging may be desirable.
Further, because full spatial imaging of autofluorescence is performed, with preferably the same field of view as the visual light imaging, the spatial extent of abnormal tissue can be determined in the analysis mode, as opposed to point spectroscopy, which would require point by point examination to determine the boundaries of the abnormal tissue, which would be much slower, and may miss points.
With this invention, full spatial data and only selected spectral data are collected, because only the differentiating portions necessary for spectral analysis are collected. Thus, xe2x80x9cpushbroomxe2x80x9d imaging is like older low-speed photocopiers, scanners and fax machines, while full-area imaging is like modem high-speed photocopiers, and is made even faster by collecting only the selected spectral data necessary to differentiate normal from abnormal tissues. This makes analysis faster, reducing patient movement, discomfort and blurring.
If a polarizing filter is used in this system, analysis speed can also be increased. A polarizing filter (such as an acousto-optical tunable filter (AOTF) or liquid crystal tunable filter (LCTF) or other filter that uses polarization) both diverts (diffracts) and transmits separate portions (usually approximately half each) of the light that is inputted, based on the polarization. The transmitted light portion can be separated and used to increase the diverted signal in several ways, such as by changing the polarization of the light that would be transmitted to match the polarization of the light that would be diverted (using means known to those skilled in the art, or other device now known or later invented) before it passes through the filter, and then recombining the light, or other means known to those skilled in the art. With increased optical throughput, the time for analysis of autofluorescence is correspondingly decreased.